Nearly 50 percent of human tumors contain p53 point mutations in the DNA-binding core domain, which often cause accumulation of p53 due to stabilization. Mutated p53 is deficient for sequence-specific DNA-binding and does not activate target genes such as p21/WAF1, Bax, and MDM2. Mutant p53 can be tethered to the promoters of certain growth-promoting genes such as PCNA and c-myc by unknown mechanisms and may stimulate cell proliferation. High-level expression of mutant p53 in a large percentage of human tumors presents an attractive target for therapeutic intervention. Recent studies show that certain mutant p53 proteins can be reactivated by second site mutations, Pab421 antibody binding, a C terminal peptide, and a novel class of small molecules represented by CP31398. We have recently found that the plant alkaloid ellipticine can efficiently restore wild type p53-1ike transcription function to a panel of p53 hot spot mutants. Ellipticine induces p53 downstream target p21/WAF1 and MDM2 expression in a mutant p53-dependent manner and has no effects on the activity of wild type p53 or p53 homologs p63 and p73. Ellipticine treatment alters mutant p53 conformation and sensitivity to protease digestion. We hypothesize that ellipticine rescues mutant p53 by binding and inducing the correct folding of p53. Furthermore, rescue of mutant p53 folding may reduce p53-hsp90 interaction, which in turn promotes MDM2-ARF interaction and translocation of MDM2 to the nucleolus. We propose the following specific aims to test these hypotheses and investigate the biological significance of mutant p53 rescue by ellipticine. (1) Investigate the mechanism of mutant p53 activation by ellipticine. (2) Determine the mechanism of MDM2 nucleolar translocation induced by ellipticine. (3) Screen for more potent ellipticine derivatives. (4) Test the effects of activating mutant p53 in tumor xenograft models. These experiments will lead to a better understanding of the mechanism of mutant p53 rescue and the potential of ellipticine and its derivatives in specifically targeting tumors with p53 mutations. The information will also help to develop more specific and potent agents that can be tested in the clinic.